Stereoselective esterase from Aspergillus oryzae

ABSTRACT

An esterase isolated from  Aspergillus oryzae  is capable of stereoselective hydrolysis of chiral esters and also has arylesterase activity (EC 3.1.1.2) and feruloyl esterase activity (EC 3.1.1.73). The esterase has only a limited homology to known amino acid sequences.

This application is a 35 U.S.C. 371 national application of PCT/DK/01/00508 filed Jul. 19, 2001, which is a continuation-in-part of U.S. application Nos. 09/633,613 now abandoned and 09/633,890, now abandoned both filed Aug. 7, 2000 and claims priority or the benefit under 35 U.S.C. 119 of PCT application nos. PCT/DK00/00439 and PCT/DK00/00440, Danish application no. PA 2001 00088, and U.S. provisional application No. 60/263,364 filed Aug. 7, 2000, Aug. 7, 2000, Jan. 17, 2001, and Jan. 23, 2001, respectively, the contents of which are fully incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to an esterase, to methods of using and producing it, and to a nucleic acid sequence encoding it. The esterase is capable of stereoselective hydrolysis of chiral esters and of hydrolyzing ferulic acid esters.

BACKGROUND OF THE INVENTION

It is known to prepare chiral esters of high optical purities by asymmetric hydrolysis with enzymes. Thus, U.S. Pat. No. 4,587,462 discloses asymmetric hydrolysis of lower alkyl esters of naproxen with a microbial enzyme, particularly a specific splitting esterase from Aspergillus oryzae DSM 2808 (ATCC 11492). U.S. Pat. No. 5,155,028 discloses enzymatic stereoselective ester cleavage using lipases, esterases or proteases, e.g. lipases or esterases from Aspergillus or proteases from Aspergillus oryzae. JP 7-206756 A discloses use of an enzyme to prepare optically active compounds. The enzyme may be a protease or esterase produced by Aspergillus, e.g. from A. oryzae.

Enzymes with ferulic acid esterase activity are known, e.g., from Aspergillus oryzae. M. Tenkanen, Biotechnology and Applied Biochemistry, 27 (1), 19–24 (1998)); M. Tenkanen et al., J. Biotechnol., 18 (1–2), 69–84 (1991).

U.S. Pat. No. 5,516,679 discloses a penicillin V amidohydrolase from Fusarium oxysporum.

SUMMARY OF THE INVENTION

The inventors have isolated an esterase from Aspergillus oryzae which is capable of stereoselective hydrolysis of chiral esters and also has arylesterase activity (EC 3.1.1.2) and feruloyl esterase activity (EC 3.1.1.73). The novel esterase has only a limited homology to known amino acid sequences. The inventors also isolated a gene encoding the novel esterase and cloned it into an E. coli strain.

Accordingly, the invention provides an esterase which may be a polypeptide having an amino acid sequence as the mature peptide shown in SEQ ID NO: 2 or which can be obtained therefrom by substitution, deletion, and/or insertion of one or more amino acids.

Further, the esterase of the invention may be a polypeptide encoded by the esterase encoding part of the DNA sequence cloned into a plasmid present in Escherichia coli deposit number DSM 13977.

The esterase may also be an analogue of the polypeptide defined above which:

i) has at least 50% identity with said polypeptide,

ii) is immunologically reactive with an antibody raised against said polypeptide in purified form,

iii) is an allelic variant of said polypeptide,

Finally, the esterase of the invention may be a polypeptide which is encoded by a nucleic acid sequence which hybridizes at 60° C., 2×SSC, 0.5% SDS with the complementary strand of nucleotides 572–911 and 971–2208 of SEQ ID NO: 1 or a subsequence thereof of at least 100 nucleotides.

The nucleic acid sequence of the invention may comprise a nucleic acid sequence which encodes the esterase described above, or it may encode an esterase and comprise:

a) the esterase encoding part of the DNA sequence cloned into a plasmid present in Escherichia coli DSM 13977,

b) nucleotides 629–911 and 971–2208 of SEQ ID NO: 1 (encoding the mature polypeptide), or

c) an analogue of the DNA sequence defined in a) or b) which

i) has at least 60% identity with said DNA sequence, or

ii) hybridizes at 60° C., 2×SSC, 0.5% SDS with the complementary sequence of said DNA sequence.

Other aspects of the invention provide a recombinant expression vector comprising the DNA sequence, and a cell transformed with the DNA sequence or the recombinant expression vector.

A comparison with full-length prior-art sequences shows the closest known sequence is a penicillin V amidohydrolase from Fusarium oxysporum (U.S. Pat. No. 5,516,679). The mature amino acid sequence of the invention has 48% identity to the known sequence, and the corresponding DNA sequences have 54% identity.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a restriction map of the esterase expression plasmid pCaHj585.

DETAILED DESCRIPTION OF THE INVENTION

Genomic DNA Source

The esterase of the invention may be derived from strains of Aspergillus, particularly strains of A. oryzae, using probes designed on the basis of the DNA sequence in this specification.

A strain of Escherichia coli containing a gene encoding the esterase was deposited by the inventors under the terms of the Budapest Treaty with the DSMZ Deutsche Sammlung von Microorganismen und Zellkulturen GmbH, Mascheroder Weg 1b, D-38124 Braunschweig DE on 11 Jan. 2001 under accession number DSM 13977

Recombinant Expression Vector

The expression vector of the invention typically includes control sequences encoding a promoter, operator, ribosome binding site, translation initiation signal, and, optionally, a selectable marker, a transcription terminator, a repressor gene or various activator genes. The vector may be an autonomously replicating vector, or it may be integrated into the host cell genome.

Production by Cultivation of Transformant

The esterase of the invention may be produced by transforming a suitable host cell with a DNA sequence encoding the esterase, cultivating the transformed organism under conditions permitting the production of the enzyme, and recovering the enzyme from the culture.

The host organism may be a eukaryotic cell, in particular a fungal cell, such as a yeast cell or a filamentous fungal cell, such as a strain of Aspergillus, Fusarium, Trichoderma or Saccharomyces, particularly A. niger, A. oryzae, F. graminearum, F. sambucinum, F. cerealis or S. cerevisiae. The production of the esterase in such host organisms may be done by the general methods described in EP 238,023 (Novo Nordisk), WO 96/00787 (Novo Nordisk) or EP 244,234 (Alko).

Properties and Uses of Esterase

The esterase of the invention is capable of stereoselective hydrolysis of esters including substituted esters of 3-phenyl-propanoic acids. It does not hydrolyse naproxen ethyl ester.

The esterase is useful for the preparation of optically enriched esters or acids, e.g. substituted esters of 3-phenyl-propanoic acids and substituted 3-phenyl-propanoic acids for pharmaceutical use.

The esterase also has arylesterase activity (EC 3.1.1.2) and feruloyl esterase activity (EC 3.1.1.73) and is useful in hydrolyzing feruloyl esters into ferulic acid and alcohol. It is useful for the release of ferulic acid bound to hemicellulose in the degradation of plant material and plant cell walls, e.g. as described in GB 2301103 and WO 200014234. It may also be used for the production of vanillic acid in analogy with U.S. Pat. No. 5,955,137.

Hybridization

The hybridization is used to indicate that a given DNA sequence is analogous to a nucleotide probe corresponding to a DNA sequence of the invention. The hybridization conditions are described in detail below.

Suitable conditions for determining hybridization between a nucleotide probe and a homologous DNA or RNA sequence involves presoaking of the filter containing the DNA fragments or RNA to hybridize in 5×SSC (standard saline citrate) for 10 min, and prehybridization of the filter in a solution of 5×SSC (Sambrook et al. 1989), 5× Denhardt's solution (Sambrook et al. 1989), 0.5% SDS and 100 μg/ml of denatured sonicated salmon sperm DNA (Sambrook et al. 1989), followed by hybridization in the same solution containing a random-primed (Feinberg, A. P. and Vogelstein, B. (1983) Anal. Biochem. 132:6–13), ³²P-dCTP-labeled (specific activity>1×10⁹ cpm/μg) probe for 12 hours at approx. 60° C. The filter is then washed two times for 30 minutes in 2×SSC, 0.5% SDS at a temperature of 60° C., more preferably at least 65° C., even more preferably at least 68° C.

Molecules to which the oligonucleotide probe hybridizes under these conditions are detected using a x-ray film.

Alignment and Homology

The esterase and the nucleotide sequence of the invention preferably have homologies to the disclosed sequences of at least 80% identity, particularly at least 90% identity or at least 95% identity, e.g. at least 98% identity.

For purposes of the present invention, alignments of sequences and calculation of identityscores were done using a Clustal W (J. D. Thompson et al (1994) NAR 22 (22) p 4673–4680) alignment, useful for both protein and DNA alignments. The default scoring matrices Blosum62mt2and swgapdnamt are used for protein and DNA alignments respectively. The gap opening penalty is 10 and the gap extension penalty: 0,1 for proteins.—The gap opening penalty is 15 and the gap extension penalty is 6,66 for DNA. The alignments were done using the computer programme allignX which is a component of the Vector NTI Suite 6.0 package from Informax, Inc (www.informax.com))

EXAMPLES Example 1 Preparation of a Crude Esterase Preparation from Aspergillus oryzae

Aspergillus oryzae IFO4177 was fermented using a fed-batch process with maltose/maltodextrin or glucose as the main carbon source. The batch medium contained: maltose/maltodextrin, ammonium sulphate, potassium-dihydrogenphosphate, yeast extract, beech xylan, MgSO4,7H2O, citric acid, potassium sulphate, trace metal solution and an antifoam agent. All these components were used in concentrations all being within the range of 1–18 g/L final medium. The medium pH was kept at 4.5 throughout the fermentation. The feed consisted of maltose/maltodextrin or glucose in the range of 280 g/L. 6.5 kg of batch medium was inoculated with 500 mL of seed culture. After 15–25 hours of batch fermentation the addition of feed was initiated using a feed addition rate of 15–25 g of feed per hour. This fed-batch state was continued for 100–160 hour of fermentation. Dissolved oxygen above 50% saturation was maintained by means of closed-loop control of the agitation rate. Aeration was kept at 1 volume air per volume batch medium per hour. A headspace pressure of 0.5 bar over-pressure was maintained throughout the entire fermentation. After harvest of the broth, both biomass and un-dissolved matter was removed in a filtration step. The supernatant was concentrated by removal of water using ultrafiltration, evaporation or freeze drying.

Example 2 Preparation of (2S)-2-Ethoxy-3-(4-hydroxyphenyl)propanoic acid and Ethyl (2R)-2-Ethoxy-3-(4-hydroxyphenyl)propanoate

Ethyl (2RS) (+/−) 2-ethoxy-3-(4-hydroxyphenyl)propanoate (0.5 g) was shaken with 60 mg of the lyophilised esterase preparation from Aspergillus oryzae in 1 ml 1M phosphate buffer (pH=7) with organic co-solvents (according to the table below) at 27° C. The reaction mixture was poured into 20 ml MeOH after 4 h to stop the enzymatic reactions followed by analysis by chiral capillary electrophoresis to determine the enantiomeric excess (ee) as follows:

HP 3D Capillary Electrophoresis and 80.5/72.0 cm, 50 mm HP bubble capillary were used. The electrolyte was HS-β-CD (Regis) (2% w/v) and TM-β-CD (Sigma) (2% w/v) in 25 mM borate buffer pH 9.3 (HP). The reaction mixture was diluted approximately 25 times in borate buffer 5 mM, pH 9.3 (or final concentration ca. 0.025 mg/ml–0.1 mg/ml) and injected (50 mbar in 4.0 seconds). The applied voltage was 30 kV.

Co-solvent Product_(acid) (%) (ee)_(acid) (%) Acetone/0.1 ml 37 93 Acetone/0.3 ml 31 94 THF/0.1 ml 36 94 THF/0.2 ml 31 93 THF/0.3 ml 21 91 2-Propanol/0.1 ml 36 97 2-Propanol/0.3 ml 27 93 Ethanol/0.1 ml 35 96 Ethanol/0.2 ml 32 96 Ethanol/0.3 ml 22 93

Example 3 Preparation of (2S)-2-Ethoxy-3-(4-hydroxyphenyl)propanoic acid and Ethyl (2R)-2-Ethoxy-3-(4-hydroxyphenyl)Propanoate

Ethyl (2R/S) (+/−) 2-ethoxy-3-(4-hydroxyphenyl)propanoate (5 g) was added to an aqueous 0.1 M phosphate buffer pH 7 (10 ml). 100 mg of the lyophilised esterase preparation from Aspergillus oryzae was added and the mixture was stirred for 18 hours at room temperature. During that time, the pH of the reaction mixture was kept constant at pH=6-8 by addition of NaOH. Most of the water was evaporated in vacuo. Methanol was added to the remaining slurry in order to stop the hydrolysis. The precipitate, which formed was filtered off and the methanol was evaporated in vacuo. The remaining oil was dissolved in water followed by extraction of unreacted ester with tert-butyl methyl ether (TBME) (ee_(ester)=87%, determined as in Example 2). The water phase was acidified to pH=3 and the acid extracted with TBME. After drying over Na₂SO₄ and evaporation of the TBME, 1.8 g (2S)-2-Ethoxy-3-(4-hydroxyphenyl)propanoic acid was obtained as an oil, which crystallized on standing (m.p.=105° C., ee_(acid)=>99%, determined as in Example 2).

Example 4 Purification of the Esterase

Fermentation of Asperqillus oryzae IFO4177

Fed batch fermentation of a derivative of Aspergillus oryzae IFO4177 was performed in a medium comprising maltodextrin as a carbon source, urea as a nitrogen source and yeast extract. The fed batch fermentation was performed by inoculating a shake flask culture of A. oryzae into a medium comprising 3.5% of the carbon source and 0.5% of the nitrogen source. After 24 hours of cultivation at pH 5.0 and 34° C. the continuous supply of additional carbon and nitrogen sources were initiated. The carbon source was kept as the limiting factor and it was secured that oxygen is present in excess. The fed batch cultivation was continued for 4 days, after which the enzyme was recovered by centrifugation, ultrafiltration, filtration, germ filtration and spray drying.

Assay for Ester Hydrolysis:

The assay is an pH indicator based assay, where the decrease in pH is measured with p-Nitrophenol, when the enzyme cleaves the ester Ethyl (2RS) (+/−) 2-ethoxy-3-(4-hydroxyphenyl)propanoate. The buffer capacity of the enzyme sample in question has to be low, as a high buffer capacity in the sample will suppress the pH drop.

50 μl enzyme (diluted in 5 mM BES (Sigma B-6420), pH 7.1) was mixed with 100 μl Assay solution (a mixture of 400 μl Ethyl (2RS) (+/−) 2-ethoxy-3-(4-hydroxyphenyl)propanoate (55 mM in acetonitril), 2000 μl 5 mM p-Nitrophenol in 5 mM BES, pH 7.1 and 7600 μl 5 mM BES, pH 7.1). After a 5 minutes lag period, the decrease in OD₄₀₅ the next 10 minutes was monitored as a measurement of the enzyme activity. If the slope of the monitored curve deviated from linearity, the assay was repeated with a higher enzyme dilution.

Purification of the Esterase

24 g of a spray dried Aspergillus oryzae IFO4177 supernatant was dissolved in 375 ml 5 mM CH₃COOH/NaOH, pH 4.0 and the pH was adjusted to pH 4.0. The solution had a 1 mS/cm conductivity. The solution was applied to a 100 ml S-sepharose FF column (Amersham Pharmacia Biotech) equilibrated in 25 mM CH₃COOH/NaOH, pH 4.0. After washing the column with the same buffer, the column was eluted with a linear NaCl gradient from 0 to 0.5M over 5 column volumes. Fractions (10 ml) from the column were analyzed for esterase activity and fractions 42–46 were pooled. The 42–46 pool was dialysed over night against 10 mM KH₂PO₄/NaOH, pH 7.0 in dialysis tubing and then applied to a 40 ml Q-sepharose FF column (Amersham Pharmacia Biotech) column equilibrated in 20 mM KH₂PO₄/NaOH, pH 7.0. After washing the column with the same buffer, the column was eluted with a linear NaCl gradient from 0 to 0.25M over 5 column volumes. Fractions from the column were analysed for activity. The activity was found in the unretained fraction. The pH of the unretained fraction was adjusted to pH 8.0 and applied to the same 40 ml Q-sepharose FF column, but this time equilibrated in 20 mM HEPES/NaOH, pH 8.0. After washing the column with the HEPES buffer, the column was eluted with a linear NaCl gradient from 0 to 0.25M over 5 column volumes. Fractions (4 ml) from the column were analysed for activity and fractions 18–22 were pooled. The 18–22 pool was diluted 10 times with deionised water and applied to an 8 ml SOURCE Q column (Amersham Pharmacia Biotech) equilibrated in 20 mM HEPES/NaOH, pH 8.0. After washing the column with the same buffer, the column was eluted with a linear NaCl gradient from 0 to 150 mM over 30 column volumes. Fraction (3 ml) 28 and 29 was pooled and applied to a 300 ml Superdex75 column (Amersham Pharmacia Biotech) equilibrated in 20 mM HEPES/NaOH, 200 mM NaCl, pH 8.0. The Superdex75 column was eluted with the same buffer and fractions (5 ml) were analyzed for activity. The enzyme activity peaked in fraction 6 and 7. Fraction 5, 6, 7 and 8 were concentrated to approx. 70 μl in 10 kDa cut-off polysulfone Ultrafuge units (ultrafiltration by centrifugation). 10 μl of each fraction were applied to a SDS-PAGE gel, and it was seen that the intensity of a ˜70 kDa band followed the activity. Fraction 6 and 7 were used for cleavage and Edman protein sequencing.

Example 5 Cleavage of the Esterase into Fragments and Sequencing of the Fragments

Reduction and Alkylation

75 μl of the purified enzyme sample was mixed with 75 μl SDS PAGE sample buffer with DTT and incubated at 37° C. for 20 min. The sample was heated to 95° C. for 3 min, cooled and subsequently 20 μl 1M Iodoacetamide (in 0.5M Tris pH 9.2) was added. Incubation for 20 min at room temperature.

In-Gel Digestion

Nine lanes in a Novex SDS-PAGE gel were loaded with the sample (all). After running the gel it was stained according to standard procedures from Novex. Pieces of the gel holding the ˜70 kDa band was subsequently cut out and minced with a blade. The gel pieces was washed 2× in 0.5M Tris pH 9.2/Acetonitrile (ACN) (1:1) for 45 min at 37° C. The gel pieces were treated with 100% ACN for 10 min to introduce shrinking of the pieces. The ACN was removed and the pieces dried in a speed-Vac. 200 μl 0.1M (NH₄)HCO₃ was added and incubated for 15 min. The (NH₄)HCO₃ was removed and 100 μl ACN added. Again incubation for 10 min followed by removal of ACN and drying in a speed-vac. The cycle with alternating (NH₄)HCO₃ and ACN addition/removal was repeated 2×. After the last drying step 25 μl 0.1 μg/μl Acromobacter lysyl endopeptidase in 0.1M Tris pH 9.2, 10% ACN was added. Incubation for 20 min. Then 350 μl 0.1M Tris pH 9.2, 10% ACN was added. Incubation was continued over night at 37° C.

Then 40 μl 10% Trifluoroacetic acid (TFA) was added and after a 10 min incubation, the supernatant was removed (saved for control). Extraction of peptides was done 2× by adding 200 μl 0.1% TFA, 60% ACN to the gel pieces and incubate for 45 min at 37° C. All extracts were collected (65 μl+200 μl+200 μl) and concentrated in the speed-vac to 50 μl. 50 μl 0.1% TFA was added and the sample re-dried to 50 μl.

Separation of Peptides

The sample was run on RP-HPLC on a 2×50 mm Vydac C-18 column using a TFA/ACN solvent system (gradient from 0% to 64% ACN in 0.1% TFA over 31 min, 150 μl/min, detection at 214 nm). Controls with blank gel pieces were run in parallel. Selected peptides from the separation were subjected to sequence analysis by Edman degradation.

Peptide Sequences

Sequence analysis of the peptides showed that three sequences was obtained. The determined sequences were denoted 161299Afr15 (SEQ ID NO: 3), 161299Afr17 (SEQ ID NO: 4) and 161299Afr23 (SEQ ID NO: 5).

Example 6 Cloning of the Esterase Gene

Partial Cloning of the Esterase Gene by PCR.

The three peptide sequences determined in example 5 were all found to show some homology to a Penicillin V amidohydrolase from Fusarium oxysporum (GeneSeqP: W00290). Thus, 161299Afr15 (SEQ ID NO: 3), 161299Afr17 (SEQ ID NO: 4) and 161299Afr23 (SEQ ID NO: 5) could be aligned with amino acids 381–398, 349–366 and 181–201, respectively, of GeneSeqP: W00290.

Based on this alignment, two PCR primers were designed to PCR amplify a part of the A. oryzae esterase gene.

A primer (B2716F09, SEQ ID NO: 6) corresponding to the sense direction protein sequence of peptide 161299Afr23 (amino acids 13–21 of SEQ ID NO: 5) was synthesized.

A primer (B2716F11, SEQ ID NO: 7) corresponding to the antisense direction of the protein sequence of peptide 161299Afr15 (amino acids 4–12 of SEQ ID NO: 3) was synthesized.

These two PCR primers were used for amplification of an esterase gene fragment in the following way:

Genomic DNA was prepared from Aspergillus oryzae IFO 4177 as described by Yelton et. al. (M. M. Yelton, J. E. Mamer and W. E. Timberlake (1984) Proc. Natl. Acad. Sci. USA 81, 1470–1474).

The Expand PCR system (Roche Molecular Biochemicals, Basel, Switzerland) was used for the amplification following the manufacturers instructions for this and the subsequent PCR amplifications. The magnesium concentration was held at 2.5 mM in all PCR reactions.

The following thermal cycling program was run on an MJ Research PTC 150 thermal cycler:

94° C. for 1 min. 1 cycle 94° C. for 10 sec. Temperature ramping at −0.5° C./sec. 50° C. for 10 sec. 40 cycles 72° C. for 30 sec. 72° C. for 1 min. 1 cycle.

A PCR product of approx. 550 bp were detected on a 1% agarose gel. This fragment was recovered and cloned into the pCR4-TOPO vector following the manufacturers instructions (Invitrogen BV, Groningen, the Netherlands).

A plasmid with an insert of the expected size, pCaHj571, was selected for sequencing and it was sequenced using the following primers: −48 reverse (SEQ ID NO: 8) and −40 universal (SEQ ID NO: 9).

All sequence reactions were made using BigDye™ Terminator Cycle Sequencing Kits from the Perkin-Elmer Corporation (USA), and the reactions were run on an ABI 3700 capillary sequencer from the Perkin-Elmer Corporation following the manufacturers instructions.

The sequence encoded a protein sequence homologous to the F. oxysporum amidohydrolase and also encoded the peptide sequence 161299Afr17, and it was thus concluded that the amplified fragment is a part of the esterase gene. The sequence of the PCR fragment is shown as SEQ ID NO: 27.

Genomic Cloning of the Esterase Gene.

A cosmid library of A. oryzae IFO4177 has previously been prepared as described in WO 9801470.

The insert of pCaHj571 was labelled with DIG by using the plasmid as template in a PCR reaction together with the primers B2716F09 and B2716F11 and the PCR DIG probe synthesis kit from Roche Molecular Biochemicals following the manufacturers instructions.

The DIG labeled fragment was used to probe filters of the cosmid library using the recomandations of Roche Molecular Biochemicals, and the hybridization signals were visualized using CSPD detection following the instructions of Roche Molecular Biochemicals and using a LAS1000 plus CDC camera manufactured by Fujifilm.

One cosmid giving a clear hybridization signal was isolated and termed pCaHj577.

A southern blot using genomic DNA of A. oryzae IFO4177 was done using the same probe, hybridization conditions and detection method as for the cosmid isolation. The DNA was digested with the restriction enzymes BamH I, BglII, EcoR I, Hind III, Mlu I, Mun I, Sac I, SaL I or Xho I. In addition an Asp 718 digestion was made, and double digestions of Asp 718 and the list of enzymes just indicated was made.

The Southern blot indicated that the 5′ end of the esterase gene was present on an approx. 1.4 kb Asp718 fragment. The 3′ end of the gene appeared to be present on an approx 2 kb Mun I—EcoR I fragment.

The 5′ and the 3′ end of the gene was cloned by inverse PCR in the following way:

From the sequence given in SEQ ID NO: 27, the following PCR primers were designed: B2998F06 (SEQ ID NO: 10), B3591G12 (SEQ ID NO: 11) and B2998F07 (SEQ ID NO: 12).

For the 5′ inverse PCR 500 ng of pCaHj577 was digested with Asp718, and the formed fragments were separated on a 1% agarose gel. Fragments of approx. 1.4 kb were recovered from the gel and dissolved in a total volume of 0.5 ml. Ligation buffer and T4 DNA ligase (Roche Molecular Biochemicals) was added and the solution was incubated at 16° C. for approx. 18 hours. The mixture was concentrated by ethanol precipitation and the ligation product was used as template in a PCR reaction using the primers B2998F06 and B3591G12 and the PCR conditions described in the previous section. A PCR product of approx. 1 kb was detected on a 1% agarose gel. This fragment was recovered and cloned into the pCR4-TOPO vector. Sequencing of one of the formed plasmids demonstrated the insert to be the 5′ end of the esterase. This plasmid was named pCaHj578.

For the 3′ inverse PCR 500 ng of pCaHj577 was digested with Mun I and EcoR I, and the formed fragments were separated on a 1% agarose gel. Fragments of approx. 2 kb were recovered from the gel and dissolved in a total volume of 0.5 ml. Ligation and concentration was done as with the 5′ end. The ligation product was used as template in a PCR reaction using the primers B2998F06 and B2998F07. A PCR product of approx. 1.1 kb was detected on a 1% agarose gel. This fragment was recovered and cloned into the pCR4-TOPO vector. Sequencing of one of the formed plasmids demonstrated the insert to be the 3′ end of the esterase. This plasmid was named pCaHj579.

Sequencing of the Esterase Gene.

The esterase gene was sequenced using the plasmids pCaHj571, pCaHj 577, pCaHj578 and pCaHj579 as templates and the following primers:

−48 reverse (SEQ ID NO: 8), −40 universal (SEQ ID NO: 9), B2998F06 (SEQ ID NO: 10), B3591G12 (SEQ ID NO: 11), B2998F07 (SEQ ID NO: 12), B3864E07 (SEQ ID NO: 13), B3864E08 (SEQ ID NO: 14), B3998D09 (SEQ ID NO: 15), B3998D10 (SEQ ID NO: 16), B3998D11 (SEQ ID NO: 17), and B3591G11 (SEQ ID NO:18).

All sequence reactions were made using BigDye™ Terminator Cycle Sequencing Kits from the Perkin-Elmer Corporation (USA), and the reactions were run on an ABI 3700 capillary sequencer from the Perkin-Elmer Corporation following the manufacturers instructions.

The sequence is shown together with the translation as SEQ ID NO: 1. A single intron was predicted by the computer programme NetGene2 (P. G. Korning et. al (1996) Nucl. Acids. Res. 24: 3439–3452).

By analysis of the protein sequence a secretory signal sequence was predicted using the computer programme SignalP (H. Nielsen et al (1997) Protein Eng. 10: 1–6).

Example 7 Expression of the Esterase Gene

The Aspergillus expression plasmid pCaHj527 (WO 0070064) consists of an expression cassette based on the Aspergillus niger neutral amylase II promoter fused to the Aspergillus nidulans triose phosphate isomerase non translated leader sequence (Pna2/tpi) and the Aspergillus niger amyloglycosidase terminater (Tamg). Also present on the plasmid is the Aspergillus selective marker amdS from Aspergillus nidulans enabling growth on acetamide as sole nitrogen source and the URA3 marker from Saccharomyces cerevisiae enabling growth of the pyrF defective Escherichia coli strain DB6507 (ATCC 35673). Transformation into E. coli DB6507 using the S. cerevisiae URA 3 gene as selective marker was done in the following way:

E. coli DB6507 was made competent by the method of Mandel and Higa (Mandel, M. and A. Higa (1970) J. Mol. Biol. 45, 154). Transformants were selected on solid M9 medium (Sambrook et. al (1989) Molecular cloning, a laboratory manual, 2. edition, Cold Spring Harbor Laboratory Press) supplemented with 1 g/l casaminoacids, 500 μg/l thiamine and 10 mg/l kanamycin.

PCaHj527 was modified in the following way:

ThePna2/tpi promoter present on pCaHj527 was subjected to site directed mutagenises by a simple PCR approach.

Nucleotide 134–144 was altered from SEQ ID NO: 19 to SEQ ID NO: 20 using the mutagenic primer 141223 (SEQ ID NO: 21).

Nucleotide 423–436 was altered from SEQ ID NO: 22 to SEQ ID NO: 23 using the mutagenic primer 141222 (SEQ ID NO: 24).

The resulting plasmid was termed pMT 2188.

The esterase gene was cloned into pMT2188 in the following way:

The esterase gene was PCR amplified from pCaHj577 using the PCR conditions described in Example 6, except only 20 cycles was used. The primers were the following: B6093H05 (SEQ ID NO: 25) and B6093H03 (SEQ ID NO: 26).

The formed PCR fragment was digested with BamH I and Xho I, and the large fragment formed was ligated to pMT2188 digested with the same enzymes. The ligation mixture was transformed into E. coli DB6507. A plasmid from one of the colonies formed was confirmed to have the expected insert by restriction analysis and DNA sequencing. This plasmid was termed pCaHj585. A restriction map of pCaHj585 is shown in FIG. 1.

PCaHj585 was transformed into Aspergillus oryzae BECh2 (WO 0039322), fermented and recovered as described in WO 95/00636.

Example 8 Use of Esterase for Stereoselective Hydrolysis of Chiral Ester

Ethyl (2RS) (+/−) 2-ethoxy-3-(4-hydroxyphenyl)propanoate (0.5 g) was shaken with 60 mg of the lyophilised hydrolytic enzyme mixture from Aspergillus oryzae in 1 ml 1M phosphate buffer (pH=7) with organic co-solvents (according to the table below) at 27° C. The reaction mixture was poured into 20 ml MeOH after 4 h to stop the enzymatic reactions followed by analysis by the chiral CCE method 2.

Co-solvent Product_(acid) (%) (ee)_(acid) (%) Acetone/0.1 ml 37 93 Acetone/0.3 ml 31 94 THF/0.1 ml 36 94 THF/0.2 ml 31 93 THF/0.3 ml 21 91 2-Propanol/0.1 ml 36 97 2-Propanol/0.3 ml 27 93 Ethanol/0.1 ml 35 96 Ethanol/0.2 ml 32 96 Ethanol/0.3 ml 22 93

In another experiment, ethyl (2R/S) (+/−) 2-ethoxy-3-(4-hydroxyphenyl)propanoate (5 g) was added to an aqueous 0.1 M phosphate buffer pH 7 (10 ml). 100 mg of the lyophilised hydrolytic enzyme mixture from Aspergillus oryzae was added and the mixture was stirred for 18 hours at room temperature. During that time, the pH of the reaction mixture was kept constant at pH=6-8 by addition of NaOH. Most of the water was evaporated in vacuo. Methanol was added to the remaining slurry in order to stop the hydrolysis. The precipitate, which formed was filtered off and the methanol was evaporated in vacuo. The remaining oil was dissolved in water followed by extraction of unreacted ester with TBME (CCE method 2: ee_(ester)=87%). The water phase was acidified to pH=3 and the acid extracted with TBME. After drying over Na₂SO₄ and evaporation of the TBME, 1.8 g (2S)-2-Ethoxy-3-(4-hydroxyphenyl)propanoic acid was obtained as an oil, which crystallized on standing (m.p.=105° C., CCE method 2: ee_(acid)=>99%). 

1. An isolated esterase which is: (a) a polypeptide which has at least 95% identity with a polypeptide having an amino acid sequence as the mature peptide shown in SEQ ID NO: 2; (b) a polypeptide which has at least 95% identity with a polypeptide encoded by an esterase encoding part of the DNA sequence cloned into a plasmid present in Escherichia coli deposit number DSM 13977; or (c) a polypeptide which is encoded by a nucleic acid sequence which hybridizes with a complementary strand of the nucleic acid sequence shown as nucleotides 629–911 and 971–2208 of SEQ ID NO: 1 in a solution of 5×SSC, 5× Denhardt's solution, 0.5% SDS and 100 micrograms/ml of denatured sonicated salmon sperm DNA, followed by hybridization in the same solution for 12 hours at approximately 60° C., followed by washing twice for 30 minutes in 2×SSC, 0.5% SDS at a temperature of at least 65° C.
 2. The esterase of claim 1, which is native to a strain of Aspergillus.
 3. The esterase of claim 1, which is native to a strain of A. oryzae.
 4. The esterase of claim 1, which has an amino acid sequence which comprises the mature peptide shown in SEQ ID NO:
 2. 5. The esterase of claim 1, which is encoded by an esterase encoding part of the DNA sequence cloned into a plasmid present in Escherichia coli deposit number DSM
 13977. 6. The esterase of claim 1, which has an amino acid sequence which has at least 95% identity with a polypeptide encoded by an esterase encoding part of the DNA sequence cloned into a plasmid present in Escherichia coli deposit number DSM
 13977. 7. The esterase of claim 1, which has an amino acid sequence which has at least 98% identity with a polypeptide encoded by an esterase encoding part of the DNA sequence cloned into a plasmid present in Escherichia coli deposit number DSM
 13977. 8. The esterase of claim 1, which has an amino acid sequence which has at least 95% identity with the mature peptide shown in SEQ ID NO:
 2. 9. The esterase of claim 1, which has an amino acid sequence which has at least 98% identity with the mature peptide shown in SEQ ID NO:
 2. 10. The esterase of claim 1, which is encoded by a nucleic acid sequence which hybridizes with a complementary strand of the nucleic acid sequence shown as nucleotides 629–911 and 971–2208 of SEQ ID NO: 1 in a solution of 5×SSC, 5× Denhardt's solution, 0.5% SDS and 100 micrograms/ml of denatured sonicated salmon sperm DNA, followed by hybridization in the same solution for 12 hours at approximately 60° C., followed by washing twice for 30 minutes in 2×SSC, 0.5% SDS at a temperature of at least 65° C.
 11. The esterase of claim 1, which is encoded by a nucleic acid sequence which hybridizes with a complementary strand of the nucleic acid sequence shown as nucleotides 629–911 and 971–2208 of SEQ ID NO: 1 in a solution of 5×SSC, 5× Denhardt's solution, 0.5% SDS and 100 micrograms/ml of denatured sonicated salmon sperm DNA, followed by hybridization in the same solution for 12 hours at approximately 60° C., followed by washing twice for 30 minutes in 2×SSC, 0.5% SDS at a temperature of at least 68° C.
 12. A polynucleotide comprising a nucleic acid sequence which encodes the esterase of claim
 1. 13. A method for stereoselective hydrolysis of a chiral ester, comprising treating the ester with the esterase of claim
 1. 14. A polynucleotide which encodes an esterase and comprises (a) a nucleic acid sequence which has at least 95% identity with the nucleic acid sequence shown as nucleotides 629–911 and 971–2208 of SEQ ID NO: 1; (b) a nucleic acid which hybridizes with a complementary strand of the nucleic acid sequence shown as nucleotides 629–911 and 971–2208 of SEQ ID NO: 1 in a solution of 5×SSC, 5× Denhardt's solution, 0.5% SDS and 100 micrograms/ml of denatured sonicated salmon sperm DNA, followed by hybridization in the same solution for 12 hours at approximately 60° C., followed by washing twice for 30 minutes in 2×SSC, 0.5% SDS at a temperature of at least 65° C.; or (c) a complementary strand of (a) or (b).
 15. A nucleic acid construct comprising the polynucleotide of claim 14 operably linked to one or more control sequences capable of directing the expression of the esterase in a suitable expression host.
 16. A recombinant expression vector comprising the nucleic acid construct of claim 15, a promoter, and transcriptional and translational stop signals.
 17. A recombinant host cell transformed with the nucleic acid construct of claim
 15. 18. A method for producing an esterase comprising cultivating the host cell of claim 17 under conditions conducive to production of the esterase, and recovering the esterase. 